page_title: Ligand-gated ion channel
section_title: G-protein-linked receptors
hierarchical_section_title: Ligand-gated ion channel / Indirect modulation / G-protein-linked receptors
caption_attribution_description: English: Based on PDB 1CUL, PDB 1gg2, OPM 2iql &amp; OPM 2iqo and the Heller/Schaefer/Schulten lipid bilayer coordinates.
context_page_description: Ligand-gated ion channels, also commonly referred to as ionotropic receptors, are a group of transmembrane ion-channel proteins which open to allow ions such as Na⁺, K⁺, Ca²⁺, and/or Cl⁻ to pass through the membrane in response to the binding of a chemical messenger, such as a neurotransmitter.
  When a presynaptic neuron is excited, it releases a neurotransmitter from vesicles into the synaptic cleft. The neurotransmitter then binds to receptors located on the postsynaptic neuron. If these receptors are ligand-gated ion channels, a resulting conformational change opens the ion channels, which leads to a flow of ions across the cell membrane. This, in turn, results in either a depolarization, for an excitatory receptor response, or a hyperpolarization, for an inhibitory response.
  These receptor proteins are typically composed of at least two different domains: a transmembrane domain which includes the ion pore, and an extracellular domain which includes the ligand binding location. This modularity has enabled a 'divide and conquer' approach to finding the structure of the proteins.
context_section_description: Also called G protein-coupled receptor, seven-transmembrane domain receptor, 7 TM receptor, constitute a large protein family of receptors that sense molecules outside the cell and activate inside signal transduction pathways and, ultimately, cellular responses. They pass through the cell membrane 7 times. 
  G-protein-Linked receptors are a huge family that have hundreds of members identified. Ion-channel-linked receptors (e.g. GABAB, NMDA, etc.) are only a part of them.
  Table 1. Three major families of Trimeric G Proteins
caption: G-protein-coupled receptor mechanism
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